The effects of pyridine and pyrazine carboxylic acids derivatives on the growth and floral induction in duckweed (Lemna paucicostata 151) were investigated. Among the compounds which promoted the plant growth, cinchomeronic acid (CA) and trigonelline were the most effective. Picolinic acid was the strongest inhibitor of the plant growth among tested. Floral induction was observed with nicotinamide, isonicotinamide, pyrazinamide, etc. The effects of CA analogs on the growth of radish seedlings were investigated. Quinolinic acid, dinicotinic acid, and homarine increased stem elongation, but isocinchomeronic acid, dipicolinic acid, lutidinic acid, pyridine monocarboxylic acids, and pyrazine monocarboxylic acid inhibited the elongation at 10 mM. Two carboxyl groups, one at the C-3 position of the pyridine ring and the other at the C-2, C-4, or C-5 position, seem to be required for the growth promotion. The growth was inhibited by pyridine monocarboxylic acids regardless of the position of the carboxyl group, and the growth was also inhibited by pyridine dicarboxylic acids only with one carboxyl group at C-2 and the other at a position other than C-3. CA promoted hypocotyl elongation of radish seedlings when not only added to the medium but also applied directly to the hypocotyls. On microscopic observation of epidermal cells of the plant, the length of each cell was elongated several times as compared to those of the controls. The mechanism of the plant-growth promotion by CA was investigated with plasma membrane vesicle prepared from radish seedlings. CA elevated the Vmax of vanadata-sensitive H^+-ATPase in plasma membrane vesicle by 1.8 times. It was found that quinolinic acid were activators, and isocinchomeronic acid and 2, 4-lutidinic acid were inhibitors for the H^+--ATPase. These results coincided well with the effects of these compounds on the plant growth. It is suggested that CA activates ATP-dependent proton transport and leads to plant-growth promotion by the acid formed. A major metabolite of niacin in cultured tobacco cells when cultured with niacin at 1 mM was isolated and analyzed by various spectroscopic and chromatographic methods. The structure was assigned as N-(β-D-glucopyranosyl) nicotinic acid. It may be a detoxified form of excess niacin in cultured tobacco cells. Homarine is a plant-growth promoter and a morphogen in marine hydroids. A homarine-synthesizing enzyme was found for the first time in cell-free extract form turban shell (Batillus cornutus). The enzyme was purified and characterized. Some properties of the enzyme were as follows : substrates were picolinic acid and S-adenosyl-L-methionine ; optimum pH for the enzymic reaction was 6.3 ; K_m values for picolinic acid and S-adenosyl-L-methionine were 317 and 14.5 μM, respectively. The molecular weight of the enzyme was estimated to be 70,800. The enzyme activity was inhibited by heavy metal ions, S-adenosyl-L-homocysteine, adenosine, homocysteine, and sinefungin.

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α-Tocopherol, the most biologically active form of vitamin E, is a lipid soluble antioxidant that protects membranes from oxidative stresses. Vitamin E occurs in nature in eight different forms, but animal body is enriched in α-tocopherol compared with other forms. Studies on the transport of vitamin E in animals and man suggest that the liver plays a key role in the preferential retention, and subsequent distributions of α-tocopherol to tissues, but little is known about the mechanism. We have purified α-tocopherol transfer protein (αTTP) from rat liver and cloned its cDNA. αTTP specifically binds α-tocopherol and enhances its transfer between membrances. Furthermore, we have identified αTTP is abnormal in the patients with familial isolated vitamin E deficiency. In conclusion αTTP play a key role in discrimination of tocopherols as well as determination of serum vitamin E concentrations.

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